This invention relates to tags for electronic article surveillance (EAS) systems and, in particular, to EAS tags utilizing magnetically vibrating magnetic elements.
U.S. Pat. Nos. 4,510,489 and 4,510,490 disclose tags and tag structures and an EAS system in which the tags are attached to articles in order to protect the articles from theft. In the system of these patents, each EAS tag contains a first magnetic element which mechanically vibrates at a predetermined frequency in response to an interrogation field at that frequency. This vibration alters the magnetic permeability of the first magnetic element, causing the magnetic element to produce a magnetic field at the predetermined frequency. This field can then be detected to sense the tag and, thus, the article carrying the tag.
In the EAS tag of the '489 and '490 patents, a second semi-hard or hard magnetic element is also used in the tag. This second magnetic element is placed in close proximity to the first element and, when magnetized, biases or arms the first magnetic element so that it will vibrate in response to the interrogation magnetic field at the predetermined frequency. By demagnetizing the second magnetic element, the bias is removed from the first magnetic element and it no longer resonates to produce a detectable magnetic field. The tag can thus be activated and deactivated by magnetizing and demagnetizing the second magnetic element, respectively.
In the EAS tag of the '489 and '490 patents, it is essential that the first magnetic element be housed in a manner which allows it to mechanically vibrate. It is also essential that the second magnetic element be correctly situated and held in the tag in appropriate proximity to the first magnetic element, but not so as to restrict the first magnetic element's vibration. Failure to meet these requirements causes the vibration of the first magnetic element to be adversely affected, thereby preventing the tag from satisfying the desired amplitude and frequency performance criteria.
In present EAS tags of this type, the tags are formed from a plastic material which carries a heat seal coating. This material is first subjected to a thermoforming process to form a rectangular box-like housing with an open top bordered by a surrounding flange. The first magnetic element is then inserted in the housing through the open top and a plastic sheet is placed over the top and heat sealed or laminated to the border flange to close the housing and loosely encase the first magnetic element.
The second magnetic element is adhesively secured to a first side of a carrier whose second side carries an adhesively attached peelable liner. The carrier first side is laminated or otherwise secured to the plastic sheet including the part of the sheet laminated to the housing flange. With the second magnetic element thus secured via the carrier to the housing, the tag is complete. When using the tag, the liner is peeled from the carrier and the exposed adhesive surface pressed against the article, thereby securing the tag and article together.
While the aforesaid tag has proved successful, there are certain features of the tag which limit its usefulness. For example, the flange of the housing, while needed to secure the plastic sheet closing the open end of the housing, increases the housing size and for many applications is aesthetically unattractive. This prevents use of the tag with certain types of articles and, hence, in certain markets.
Also, the thermoforming and laminating procedures carried out in fabricating the tag can result in bonding of the first magnetic element to the heat seal coatings of the tag body. If this occurs, the required mechanical vibration of the first magnetic element may be restricted and the resultant tag may not perform acceptably. Tags in which this happens have to be discarded. This results in process inefficiencies and material loss.
Furthermore, the heat seal coating of the flange of the tag body remains soft after the tag manufacture is completed. As a result, during shipment of the tag, the first element may become attached or lodged against the coating. In such case, the tag will not perform satisfactorily, resulting in the return of the tag by the purchaser and reduced confidence of the purchaser in the product.
It is therefore an object of the present invention to provide an EAS tag of the above-type which does not suffer from the drawbacks of the prior tags.
It is a further object of the present invention to provide an EAS tag of the above-type which is smaller in size and aesthetically more pleasing.
It is a further object of the present invention to provide an EAS tag of the above-type which is such that the first magnetic element of the tag is less likely to be hindered by the tag body.
It is a further object of the present invention to provide an apparatus and method for making a tag meeting the above-mentioned objectives.